1. Field of the Invention
The present invention relates to wiring of data buses in a semiconductor memory unit.
2. Description of the Prior Art
In recent years, products of two or more types have been produced in one chip by changing a mere portion of a production process, for example, changing wiring at the time of assembly or changing an aluminum step in wafer process. Especially, in case change between a double data rate synchronous DRAM (DDR SDRAM) and a single data rate synchronous DRAM (SDR SDRAM) is effected, data transfer rate of the DDR SDRAM should be twice that of the SDR SDRAM and thus, the number of data buses for data transfer of the DDR SDRAM should be twice that of the SDR SDRAM. Therefore, in the SDR SDRAM, the number of unnecessary ones of the data buses increases.